Efficient characterization of semiconductor nanowires having complex dopant profiles or heterostructures is critical to fully understand these materials and the devices built from them. Existing electrical characterization techniques are slow and laborious, particularly for multisegment nanowires, and impede the statistical understanding of highly variable samples. Here, it is shown that electro‐orientation spectroscopy (EOS)—a high‐throughput, noncontact method for statistically characterizing the electrical properties of entire nanowire ensembles—can determine the conductivity and dimensions of two distinct segments in individual Si nanowires with axially encoded dopant profiles. This analysis combines experimental measurements and computational simulations to determine the electrical conductivity of the nominally undoped segment of two‐segment Si nanowires, as well as the ratio of the segment lengths. The efficacy of this approach is demonstrated by comparing results generated by EOS with conventional four‐point‐probe measurements. This work provides new insights into the control and variability of semiconductor nanowires for electronic applications and is a critical first step toward the high‐throughput interrogation of complete nanowire‐based devices.
Ensembles of semiconductor nanowires grown via the bottom-up vapor−liquid−solid (VLS) mechanism, especially those that are lightly doped or nominally undoped, can exhibit large nanowire-to-nanowire variations in electrical conductivity. This broad conductivity distribution, attributed to uncontrolled surfaces and the large surface area of nanowires, limits the fabrication of homogeneous ensembles of nanoelectronic devices, including transistors, photovoltaics, and biosensors. While methods to control surfaces are well understood for planar surfaces, the diversity of surface structures in a nanowire ensemble introduces new processing and characterization challenges. Here, we employ electro-orientation spectroscopy, a high-throughput, solutionbased method, to measure the conductivity distributions and quantify the variability of as-synthesized and postprocessed Si nanowire ensembles. Our measurements reveal a conductivity distribution with an unusual, highly skewed non-Gaussian shape, whose variability is best quantified with a log-normal coefficient of variation (COV). We demonstrate a reduction in the COV up to 2.6× as a function of increasing conformal Al 2 O 3 thickness. The decreased COV and accompanying increase in mean conductivity are consistent with a narrower distribution of surface-state densities upon passivation. Our findings highlight the surface-dependent variations inherent to bottom-up nanowire processing, and the need for advanced processes and analytical tools to control these variations for nanoelectronic applications.
The microstructure (e.g., particle orientation and chaining) of suspensions of non-spherical ferromagnetic particles can be controlled by an external field, potentially making it possible to tune the acoustic properties of the suspension. Here, we experimentally demonstrate that dilute suspensions of subwavelength-sized oblate-spheroidal nickel particles exhibit up to a 35% change in attenuation coefficient at MHz frequencies upon changing the direction of an external magnetic field, for particle volume fractions of only 0.5%. Comparison is made to suspensions of spherical particles, in which the attenuation is smaller and nearly isotropic. Optical transmission measurements and analysis of the characteristic timescales of particle alignment and chaining are also performed to investigate the reasons for this acoustic anisotropy. The alignment of the oblate-spheroidal particles is found to be the dominant mechanism for the anisotropic and tunable acoustic attenuation of these suspensions.
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